Analysis of the carbon-13 n.m.r. spectrum of hydrolyzed O-(carboxymethyl)cellulose: monomer composition and substitution patterns

The effects of O-carboxymethylation at each of positions 2, 3, and 6 on the 13C chemical shifts of glucose have been used to assign first the 13C-n.m.r. spectra of 2,3-, 2,6-, and 3,6-di-O-(carboxymethyl)glucose and 2,3,6-tri-O-(carboxymethyl)-glucose and then the spectrum of hydrolyzed O-(carboxymethyl)cellulose (CMC). Quantitative analysis of the latter spectrum yields the composition of CMC in terms of the mole fractions of the eight component monomeric residues. The results on the monosaccharide composition for a series of samples having degrees of substitution in the range 0.55–2.17 are described well by Spurlin's statistical kinetic model for the arrangement of substituents (substitution pattern) in cellulose derivatives. The model assumes that the substitution pattern is governed by the relative rate-constants for reaction of the three hydroxyl groups in the glucose residue. The values of the constants determined in this work are k2 : k3 : k6 = 2.14 : 1.00 : 1.58.